1. Field of the Invention
The present invention generally relates to liquid level gauges and, more particularly to early flood detection and warning systems which are used to determine threat of flash flood or stage flood, and provide sufficient early warning to potential victims in the affected area.
2. Description of the Prior Art
An early flood warning system requires a highly reliable liquid level measuring device for measuring rainfall and/or stream level. Existing liquid level measuring devices employ float switches, mechanical tipping mechanisms, some type of mechanical to electrical transduction, or measurement of a variable liquid characteristic such as resistance, capacitance, or inductance to determine the level of the liquid being measured. Any type of mechanical mechanism may be damaged or otherwise rendered inaccurate by environmental factors, foreign objects or debris carried in the liquid, vibration, or accidental device mishandling. Measurement of an electrical variable such as resistance, capacitance or inductance is subject to variation due to temperature, and changes in the composition of the liquid being measured. Existing early flood warning systems utilize rain and stream level gauges which suffer these and other significant disadvantages.
Rain gauges most commonly in use are either manual types, which require constant monitoring by personnel, or automated tipping bucket types. The latter of these depends on a very delicate reciprocating balance to determine the amount of rainfall by weight. The tipping action activates switches, which record the events on a strip chart or similar recording device. The delicate nature of this mechanical mechanism makes it extremely susceptible to damage and/or inaccuracy do to vibration, deposited debris, and/or vandalism. Furthermore, permanent data loss can occur if recording of, or transmission of the tipping action is interrupted, since one such event is indistinguishable from another.
Stream level gauges which sound alarms or the like, when the water level reaches a predetermined critical level, do not provide necessary advanced warning for areas near the gauge site, nor does the gauge provide information from which stream level rise rate can be accurately calculated. Malfunction of the single level detector (usually a float switch) can result in failure of the entire warning system. Existing multilevel stream gauges which use float switches as level detectors, can be damaged by debris carried in the stream water, causing malfunction of the gauge. In order to protect delicate float mechanisms from such damage and to achieve reliable recording of stream level, costly stilling basin installations are required. Existing rain and stream level gauges do not distinguish between short term level transient conditions caused by vibration, splashing or wave motion, and a longer term genuine level change. Electronic gauges which rely on analog circuits to accomplish level measurement are highly susceptible to inaccuracy due to power supply and temperature variations.
Previously proposed flood warning systems which automatically collect rainfall and stream level data do so by using polling or interrogating schemes, whereby at predetermined intervals a signal from a central facility is conveyed to each of the gauges in a network, interrogating the current gauge status. Such systems are unnecessarily costly since they require two-way communication networks. In order to achieve adequate and reliable data collection these systems must interrogate the gauges frequently regardless of the prevailing meteorological conditions. Such frequent interrogations and gauge responses introduce undesirable and unnecessary radiant energy into the environment, and needlessly consume valuable energy. Remotely located gauges must also be connected to power lines, or contain very large energy storage facilities in order to sustain frequent data transmission demands of such a system. An additional disadvantage of such polling schemes is that large quantities of redundant data are collected during extended periods of little or no adverse meteorological activity.
Furthermore, existing systems do not integrate the functions of rainfall and stream level monitoring with effective warning systems so that with existing systems critically valuable time is lost between data collection and flood prediction and subsequent warning to potential victims.
A need therefor exists for a new Early Flood Warning System which does not suffer the above disadvantages and limitations, and which contains: a network of automated digital liquid level gauges specially adapted to operate as rain and stream level gauges; data analysis facilities; and disaster alert devices.